Internal combustion engines may include water injection systems that inject water from a storage tank into a plurality of locations, including an intake manifold, upstream of engine cylinders, or directly into engine cylinders. Injecting water into the engine intake air may increase fuel economy and engine performance, as well as decrease engine emissions. When water is injected into the engine intake or cylinders, heat is transferred from the intake air and/or engine components to the water. This heat transfer leads to evaporation, which results in cooling. Injecting water into the intake air (e.g., in the intake manifold) lowers both the intake air temperature and a temperature of combustion at the engine cylinders. By cooling the intake air charge, a knock tendency may be decreased without enriching the combustion air-fuel ratio. This may also allow for a higher compression ratio, advanced ignition timing, and decreased exhaust temperature. As a result, fuel efficiency is increased. Additionally, greater volumetric efficiency may lead to increased torque. Furthermore, lowered combustion temperature with water injection may reduce NOx, while a more efficient fuel mixture may reduce carbon monoxide and hydrocarbon emissions. As mentioned above, water may be stored in a vehicle to provide water for injection on demand. However, in order to meet the water injection demands of an engine, a vehicle needs to have a sufficient supply of water. In one example, a water storage tank of a water injection may be manually refilled by a vehicle operator. However, in some situations, water for refilling the tank may not be readily available and having to re-fill the tank may be undesirable for the operator.
Other approaches to refilling a water storage tank includes collecting water (or condensate) from other vehicle systems on-board the vehicle, such as collecting water from an air conditioning (AC) of a heating, ventilation, and air conditioning (HVAC) system. For example, the approach shown by John Michael Ette in EP2607647 A1 includes extracting water from an HVAC system. Therein, collecting condensate is based on an amount of water stored in a water storage reservoir (e.g. tank) and favorable ambient conditions. Condensate is collected from an HVAC system when an ambient temperature is high and a water storage tank level is below a level for water injection demand. However, the inventors have recognized potential issues with such methods. In particular, collecting water from an HVAC system only when ambient conditions are conducive for condensate production may be insufficient to meet the water injection demands of an engine. Further, operating an AC compressor of the HVAC system when ambient conditions are favorable but AC has not been requested in order to collect condensate may require additional fueling and diminish the fuel economy benefit of water injection.
In one example, the issues described above may be addressed by a method for a vehicle including adjusting a position of an air recirculation valve of a HVAC system of the vehicle to vary a ratio of fresh ambient air to recirculated cabin air routed through an AC evaporator of the HVAC system based on level of water in a water reservoir coupled to a water injection system. A water injection system, including the water reservoir, may be fluidly coupled to the HVAC system. Thus, when the AC compressor is run (e.g., as the AC compressor load increases), the HVAC recirculation valve may be adjusted and water may be collected from the AC system of the HVAC system. The position of the HVAC recirculation valve may be adjusted to adjust the ratio of ambient to recirculated air directed to the AC evaporator based on a determined ambient air humidity and recirculated air humidity in response to a water level in the water reservoir. Collected water is then stored at the water reservoir for use in the water injection system. In this way, the air recirculation valve is adjusted while the AC compressor is running to collect water for a water injection system, thereby providing water for injection via the injection system. For example, adjusting the position of the HVAC air recirculation valve may include decreasing a ratio of ambient air to recirculated cabin air to increase an amount of recirculated cabin air routed through the AC evaporator, in response to the water level in the water reservoir (e.g. tank) being less than a threshold level and a determination of a higher recirculated air humidity relative to an ambient air humidity. Additionally, this may include adjusting a position of the HVAC recirculation to a position that is different from a vehicle operator selected position based on a desired position for water collection and cycling the AC compressor to provide a passenger requested cabin temperature. In this way, the position of the HVAC air recirculation valve may be adjusted during AC operation in order to increase an amount of condensate collected. As a result, a greater quantity of condensate may be collected from the HVAC system over a wider range of vehicle and ambient operating conditions to provide water for the water injection system. Additionally, the water level in the water reservoir of the water injection system may be replenished automatically without manual filling and may be maintained at sufficient levels for water injection system operation. Further, by reducing the likelihood of running out of water or running the AC compressor for water collection when AC is not requested, more water may be available for water injection and/or less power may be consumed by the AC compressor, thereby improving fuel economy.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.